Berthold Hoffmann Abstraction and Control for Shapely Nested Graph Transformation. 39-65 2003 58 Fundam. Inform. 1 http://iospress.metapress.com/openurl.asp?genre=article&issn=0169-2968&volume=58&issue=1&spage=39 db/journals/fuin/fuin58.html#Hoffmann03